This invention relates to a fastening tool used to fasten an article by means of a bolt to a plasterboard or any other brittle wall whose back is inaccessible.
It is usually impossible to fasten an object to a brittle wall such as a plasterboard by simply driving a nail or screw into the wall because it gets loose in the wall. To prevent loosening of the nail or screw, it is necessary to stick a patch of reinforcing metal on the back of the wall before the wall is erected so that the nail or screw pierced through the wall can be driven into the metal patch. Once the wall is erected, it is impossible to change the position of the metal patch if the space behind the wall is limited and inaccessible. Thus, a nail or screw can be used at the predetermined position only.
In another conventional arrangement, instead of sticking a metal patch on the back of a wall before the wall is erected, a hole is drilled in a wall that has already been erected, and a bolt fastening member is inserted into the space behind the wall. With the fastening member located behind the wall, a bolt is driven through the wall and threaded into the fastening member to securely fasten an object to the wall.
If the space behind the wall is small, only a short fastening member can be inserted into this space. Such a short fastening member is correspondingly small in contact area with the wall, so that it cannot sufficiently reinforce the brittle wall. Thus, by tightening the bolt only slightly, the wall may break.
An object of the invention is to provide a fastener which can be inserted into a narrow space behind a wall, and which can be brought into contact with the back of the wall over a wide contact area to sufficiently reinforce the wall even when a bolt is tightened to fasten an object to the wall.